Process for hydroconversion of petroleum feedstocks via a slurry technology allowing the recovery of metals from the catalyst and from the feedstock using a coking step

ABSTRACT

A process for hydroconversion of heavy petroleum feedstocks comprising a hydroconversion step of the feedstock in at least one reactor containing a slurry catalyst and allowing the recovery of metals in the unconverted residual fraction, in particular those used as catalysts, The process comprises a hydroconversion step, a gas/liquid separation step, a coking step, a combustion step, a metals extraction step and a step of preparing catalytic solutions which are recycled to the hydroconversion step.

The invention relates to a process for hydroconversion of heavy petroleum feedstocks to lighter products, which can be upcycled as fuels and/or raw materials for the petrochemicals industry. More particularly, the invention relates to a process for hydroconversion of heavy petroleum feedstocks comprising a step of hydroconversion of the feedstock in at least one reactor containing a slurry catalyst and allowing the recovery of metals from the unconverted residual fraction, in particular those used as catalysts, in order to re-use them in catalytic solutions and recycle them upstream of the slurry conversion process. The process comprises a hydroconversion step, a gas/liquid separation step, a coking step, a combustion step, a metals extraction step and a step of preparing catalytic solution(s) which is/are recycled to the hydroconversion step.

Heavy petroleum feedstocks can be converted to liquid products by means of thermal treatments or hydrogenation treatments, also called hydroconversion. Current research is mainly focused on hydroconversion, as thermal treatments generally produce products of mediocre quality and a not insignificant quantity of coke.

The hydroconversion of heavy feedstocks comprises the conversion of the feedstock in the presence of hydrogen and a catalyst. Depending on the feedstock, the marketed processes use a fixed-bed technology, a bubbling-bed technology or a slurry technology. The hydroconversion of heavy feedstocks in a fixed bed or bubbling bed is carried out with supported catalysts comprising one or more transition metals (Mo, W, Ni, Co, Ru) on silica/alumina-type supports or equivalent.

For the conversion of heavy feedstocks with a particularly high content of heteroatoms, metals and asphaltenes, fixed-bed technology is generally limited, as the contaminants cause rapid deactivation of the catalyst thus requiring too high and therefore too expensive a frequency of renewal of the catalytic bed. In order to be able to treat this type of feedstock, bubbling bed processes have been developed. However, the level of conversion of the bubbling bed technologies is generally limited to levels less than 80% because of the catalytic system used and the design of the unit.

The hydroconversion technologies operating with a slurry technology provide an attractive solution to the drawbacks encountered in the use of a fixed bed or bubbling bed. In fact, the slurry technology makes it possible to treat heavy feedstocks highly contaminated with metals, asphaltenes and heteroatoms, whilst having conversion rates generally greater than 85%.

The residue slurry hydroconversion technologies use a catalyst dispersed in the form of very small particles, the size of which is less than 1 mm and preferably a few tens of microns or less (generally from 0.001 to 100 μm). Thanks to this small size of the catalysts, the hydrogenation reactions are facilitated by uniform distribution throughout the reaction zone and coke formation is greatly reduced. The catalysts, or their precursors, are injected with the feedstock to be converted at the reactor inlets. The catalysts pass through the reactors with the feedstocks and the products undergoing conversion, then they are carried along with the reaction products out of the reactors. After separation they are found in the heavy residual fraction, such as for example the unconverted vacuum residue. The catalysts used in slurry are generally sulphide catalysts preferably containing at least one element chosen from the group formed by Mo, Fe, Ni, W, Co, V and/or Ru. Generally, molybdenum and tungsten display much more satisfactory performances than nickel, cobalt or ruthenium and even more satisfactory than vanadium and iron (N. Panariti et al., Applied Catalysis A: General 204 (2000), 203-213).

Marketed technologies of hydroconversion of heavy feedstocks in slurry are known. For example the EST technology licensed by ENI, VRSH technology licensed by Chevron-Lummus-Global, HDH and HDHPLUS technologies licensed by Intevep, SRC-Uniflex technology licensed by UOP, (HC)3 technology licensed by Headwaters etc. may be mentioned

Although the small size of the catalysts in the slurry makes it possible to obtain very high conversion rates, this size proves problematic as regards the separation and recovery of the catalyst or catalysts after the hydroconversion reaction. After separation the catalysts are found in the heavy residual fraction, such as for example the unconverted vacuum residue. In certain processes, part of the vacuum residue containing the unconverted fraction and the catalysts is recycled directly to the hydroconversion reactor in order to increase the conversion yield. However, these recycled catalysts generally have no activity or very reduced activity compared with that of a fresh catalyst. Furthermore, the vacuum residue is conventionally used as fuel for the production of heat, electricity and ashes. These ashes contains the metals and is generally disposed of as waste. In this case, the metals are therefore not recovered.

Furthermore, the deactivation of the catalysts requires regular replacement thus creating a demand for fresh catalysts. The heavy feedstocks treated contain a high concentration of metals, essentially vanadium and nickel. These metals are largely removed from the feedstock by being deposited on the catalysts during the reaction. They are carried away by the catalyst particles leaving the reactor. Similarly, the deactivation of the catalysts is accentuated by the formation of coke originating in particular from the high concentration of asphaltenes contained in these feedstocks.

The continuous renewal of the catalytic phase finely dispersed in the reaction zone allows contact with the hydrogen dissolved in the liquid phase to hydrogenate and hydrotreat the heavy feedstock injected. In order to ensure a high conversion rate and maximum hydrotreatment of the feedstock, the quantity of catalytic solution to be injected is fairly significant which represents relatively high operating costs on an industrial scale. Thus, slurry hydroconversion processes generally consume large quantities of catalysts, in particular of molybdenum which represents the most active catalyst, but also the most expensive. The costs of fresh catalysts, of separation of the catalysts and of recovery of the metals have a major impact on the cost-effectiveness of such processes. The selective recovery of molybdenum and its recycling as catalyst are two elements which are essential for industrial valorization of the slurry processes. This recovery is also accompanied by that of other metals such as nickel (that injected and that recovered in the feedstock) and vanadium recovered in the feedstock, the contents of which are comparable to that of molybdenum and which can be sold for metallurgical applications.

Apart from these economic aspects, the recovery of the metals is also necessary for environmental reasons. In fact, the ashes originating from the combustion of the residual fraction has been classified as dangerous waste in a number of countries, as the metals contained in the ashes discarded as waste represent a danger to groundwater.

There is therefore a real need for recovery and recycling of the metals originating from the catalysts and heavy feedstock for the slurry hydroconversion process.

PRIOR ART

The processes of recovering metals from the slurry processes are known in the state of the art.

Thus, patent application US2008/0156700 describes a process for separating catalysts in the form of ultrafine particles originating from a slurry hydroconversion process comprising a step of precipitation or flocculation of a heavy fraction including metal parts with heptane-type solvents, a step of separation of the heavy fraction from the light fraction by centrifugation and a step of coking between 350° and 550° C. under an inert atmosphere in order to obtain coke containing the catalyst. This coke can be subjected to a metal extraction step.

U.S. Pat. No. 6,153,555 describes a process for recovery of metals, in particular molybdenum, from catalysts used in processes of hydroconversion of heavy feedstocks. This process comprises a step of coking between 300 and 1000° C., at atmospheric pressure and under an inert atmosphere. The coked product is then divided and subjected to one or two steps of combustion under air at temperatures comprised between 800 and 1900° C. in order to sublimate the molybdenum which is then condensed by cooling down on the ashes. The molybdenum is subsequently recovered by an extraction step using a mixture of liquid ammonia and (NH₄)₂CO₃.

U.S. Pat. No. 6,511,937 describes a slurry hydroconversion process for heavy feedstocks comprising, after the hydroconversion reaction, a step of separation in a high pressure, low temperature separator making it possible to separate a very light fraction, a step of deasphalting all the residual fraction using C3 to C5 paraffinic solvents at ambient temperature, a coking step (427-649° C., without air) and/or a step of combustion below 649° C. in order to produce ashes containing the catalyst. This catalyst can subsequently be subjected to steps of metal extraction and recycled in the process.

SUBJECT OF THE INVENTION

The specific nature of the slurry processes being to have a finely dispersed catalyst not supported on a mineral phase makes the recovery of the metals much more complex than that of the supported refining catalysts used conventionally. The challenge for the industrial development of the processes for hydroconversion by slurry technology is the need to recover and recycle the metals originating from the catalysts.

The present invention aims to improve the known processes of hydroconversion of heavy feedstocks by slurry technology by allowing the re-use of an unconverted residual fraction originating from the slurry conversion, a fraction with a high concentration of metals and heteroelements and finally including the recovery of said metals from said unconverted fraction and the production of catalytic precursors in order to recycle them upstream of the process for conversion in slurry mode. The process comprises a hydroconversion step, a gas/liquid separation step, a coking step, a combustion step, a metals extraction step and a step of preparing catalytic solution(s) which is/are recycled to the hydroconversion step.

Research carried out by the applicant on the hydroconversion of heavy feedstocks has led to the discovery that, surprisingly, this process comprising a separation made it possible to maximize the light fraction originating from the hydroconversion reactor and to minimize the residual fraction, coupled with a coking step, then a moderate combustion step avoiding the sublimation of the metals, making it possible to prepare the extraction of the metals contained in the ashes so that very good levels of recovery of the metals which can be recycled in the process are possible. In fact, the critical steps of this recovery are firstly the concentration of the metals on the carbon-containing matrix (via coking) then the formation of a mineral phase (via moderate combustion) containing the metallic elements originating from the catalyst (Mo and Ni) but also from the feedstock (Ni, V and Fe) devoid of carbon.

A benefit of the process according to the invention is the re-use of an unconverted residual fraction with a high concentration of metals and heteroelements allowing the recovery of said metals and the production of catalytic precursors for recycling upstream of the process for conversion in slurry mode.

Another benefit is the optimization of the hydroconversion by a gas/liquid separation after the hydroconversion taking place under operating conditions similar to those in the reactor and allowing effective separation, in a single step, of a light fraction comprising future fuel bases (gases, naphtha, light gas oil, or even heavy gas oil) from the unconverted residual fraction containing solids such as metals. The yield of the light fraction is thus maximized at the same time as the unconverted residual fraction is minimized, thus subsequently facilitating the concentration of the metals by its reduced quantity. Maintaining the operating conditions during separation also allows the economical incorporation of a subsequent hydrotreatment and/or hydrocracking treatment of the light fraction without the need for additional compressors.

Another benefit is the coking of the unconverted fraction containing metals allowing effective concentration of the metals.

Another benefit of the process is combustion at a moderate temperature making it possible to separate the organic phase from the inorganic phase containing the metals in order to facilitate the subsequent extraction of the metals from the inorganic phase while avoiding the vaporization and/or sublimation (and therefore the loss) of metals during combustion.

Another benefit of the process is that this process requires no deasphalting step and the associated drawbacks (handling of solvents which are often toxic; need for recycling the solvent after extraction etc.).

DETAILED DESCRIPTION

The invention relates to a process for hydroconversion of heavy petroleum feedstocks in slurry allowing the recovery and recycling of the metals in the unconverted residual fraction, in particular those used as catalysts.

More particularly, the invention relates to a process for hydroconversion of heavy petroleum feedstocks containing metals comprising:

a) a step of hydroconversion of the feedstock in at least one reactor containing a slurry catalyst containing at least one metal, and optionally containing a solid additive,

b) a step of separation of the hydroconversion effluent without decompression into a so-called light fraction containing the compounds boiling at a maximum temperature of 500° C. and a residual fraction,

b′) optionally a fractionation step comprising a separation under vacuum of said residual fraction as obtained in step b), and a vacuum residue with a high concentration of metals is obtained,

c) a step of coking of said residual fraction as obtained in step b) and/or of said vacuum residue as obtained in step b′) making it possible to obtain a solid effluent containing coke,

d) a step of combustion of said solid effluent containing coke at a temperature comprised between 200 and 700° C. making it possible to obtain ashes with a high concentration of metals,

e) a step of extraction of the metals from the ashes obtained in the combustion step,

f) a step of preparation of metallic solution(s) containing at least the metal of the catalyst which is/are recycled(s) as catalyst in the hydroconversion step.

Hydroconversion

The process according to the invention comprises a step of hydroconversion of the feedstock in at least one reactor containing a slurry catalyst and optionally a solid additive.

By hydroconversion is meant hydrogenation, hydrotreatment, hydrodesulphurization, hydrodenitrogenation, hydrodemetallization and hydrocracking reactions.

The heavy feedstocks concerned are petroleum hydrocarbon feedstocks such as petroleum residues, crude oils, topped crude oils, deasphalted oils, asphalts or deasphalting pitches, derivatives from petroleum conversion processes (such as for example: HCO, FCC slurry, heavy GO/coking VGO, visbreaking residue or similar thermal process etc.), bituminous sands or derivatives thereof, oil shales or derivatives thereof, or mixtures of such feedstocks. More generally, here the term “heavy feedstock” covers hydrocarbon feedstocks containing at least 50% by weight of product distilling above 250° C. and at least 25% by weight distilling above 350° C.

The heavy feedstocks concerned according to the invention contain metals, essentially V and/or Ni, generally in a quantity of at least 50 ppm by weight and most often 100-2000 ppm by weight, at least 0.5% by weight of sulphur, and at least 1% by weight of asphaltenes (heptane asphaltenes), often more than 2% by weight or also 5% by weight, levels of 25% by weight or more of asphaltenes being able to be achieved; they also contain condensed aromatic structures which can contain heteroelements resistant to conversion.

Preferably, the heavy feedstocks concerned originate from non-conventional heavy crude type oils (° API comprised between 18 and 25 and viscosity comprised between 10 and 100 cP), extra-heavy crudes (° API comprised between 7 and 20 and viscosity comprised between 100 and 10000 cP) and bituminous sands (° API comprised between 7 and 12 ° API and viscosity of less than 10000 cP) present in large quantities in the Athabasca region in Canada and the Orinoco region in Venezuela where reserves are estimated at 1700 Gb and 1300 Gb respectively. These non-conventional oils are also characterized by high contents of vacuum residue, asphaltenes and heteroelements (sulphur, nitrogen, oxygen, vanadium, nickel, etc.) requiring steps of conversion to specific commercial products of the gasoline, gas oil or heavy fuel oil type.

The heavy feedstock is mixed with a stream of hydrogen and a catalyst as dispersed as possible in order to obtain a hydrogenating activity as uniformly distributed as possible in the hydroconversion reaction zone. Preferably, a solid additive promoting the hydrodynamics of the reactor is also added. This mixture feeds the catalytic slurry hydroconversion section. This section is constituted by an oven for preheating the feedstock and the hydrogen and by a reaction section constituted by one or more reactors arranged in series and/or in parallel, depending on the required capacity. In the case of reactors in series, one or more separators can be present on the effluent at the top of each of the reactors. In the reaction section, the hydrogen can feed only one, several or all the reactors, in equal or different proportions. In the reaction section, the catalyst can feed only one, several or all the reactors in equal or different proportions. The catalyst is maintained in suspension in the reactor, flows from the bottom to the top of the reactor with the gas and the feedstock, and is removed with the effluent. Preferably, at least one (and preferably all) of the reactors is equipped with an internal recirculation pump.

The operating conditions of the catalytic slurry hydroconversion section are in general a pressure of 2 to 35 MPa, preferably 10 to 25 MPa, a partial hydrogen pressure varying from 2 to 35 MPa and preferably from 10 to 25 MPa, a temperature comprised between 300° C. and 500° C., preferably from 420° C. to 480° C., a contact time of 0.1 hour to 10 hours with a preferred duration of 0.5 hour to 5 hours.

These operating conditions coupled with the catalytic activity make it possible to obtain conversion rates per pass of the 500° C.⁺ vacuum residue which can range from 20 to 95%, preferably from 70 to 95%. The abovementioned conversion rate is defined as being the fraction by mass of organic compounds having a boiling point above 500° C. at the inlet to the reaction section minus the fraction by mass of organic compounds having a boiling point above 500° C. at the outlet from the reaction section, all divided by the fraction by mass of organic compounds having a boiling point above 500° C. at the inlet to the reaction section.

The slurry catalyst is in dispersed form in the reaction medium. It can be formed in situ but it is preferable to prepare it outside the reactor and to inject it, in general continuously, with the feedstock. The catalyst promotes the hydrogenation of the radicals originating from the thermal cracking and reduces the formation of coke. When coke is formed, it is removed by the catalyst.

The slurry catalyst is a sulphide catalyst preferably containing at least one element chosen from the group formed by Mo, Fe, Ni, W, Co, V, Ru. These catalysts are generally monometallic or bimetallic (combining for example a non-noble Group VIIIB element (Co, Ni, Fe) and a Group VIB element (Mo, W)). Preferably, NiMo, Mo or Fe catalysts are used. The catalysts used can be powders of heterogeneous solids (such as natural minerals, iron sulphate, etc.), dispersed catalysts originating from water-soluble precursors (“water soluble dispersed catalyst”) such as phosphomolybdic acid, ammonium molybdate, or a mixture of Mo or Ni oxide with aqueous ammonia. Preferably, the catalysts used originate from precursors soluble in an organic phase (“oil soluble dispersed catalyst”). The precursors are organometallic compounds such as Mo, Co, Fe, or Ni naphthenates, or such as multi-carbonyl compounds of these metals, for example Mo or Ni 2-ethyl hexanoates, Mo or Ni acetylacetonates, Mo or W salts of C₇-C₁₂ fatty acids, etc. They can be used in the presence of a surfactant in order to improve the dispersion of the metals when the catalyst is bimetallic. The catalysts are found in the form of dispersed particles, colloidal or not depending on the nature of the catalyst. Such precursors and catalysts which can be used in the process according to the invention are widely described in the literature.

In general, the catalysts are prepared before being injected into the feedstock. The process of preparation is adapted as a function of the state in which the precursor is found and its nature. In any case, the precursor is sulphided (ex-situ or in-situ) in order to form the catalyst dispersed in the feedstock. For the preferred case of the so-called oil-soluble catalysts, in a typical process, the precursor is mixed with a petroleum feedstock (which can be part of the feedstock to be treated, an external feedstock, a recycled feedstock, etc.), the mixture is optionally at least partly dried, and subsequently or simultaneously sulphided by adding a sulphur-containing compound (H₂S preferred) and heated. The preparations of these catalysts are described in the prior art.

The preferred solid additives are mineral oxides such as alumina, silica, mixed Al/Si oxides, supported spent catalysts (for example, on alumina and/or silica) containing at least one Group VIII element (such as Ni, Co) and/or at least one Group VIB element (such as Mo, W). There can be mentioned for example the catalysts described in the application US2008/177124. Carbonaceous solids with a low hydrogen content (for example 4% hydrogen), optionally pretreated, can also be used. It is also possible to use mixtures of such additives. Their particle sizes are preferably less than 1 mm. Any solid additive content present at the inlet to the reaction zone in the slurry hydroconversion process is comprised between 0 and 10% by weight, preferably between 1 and 3% by weight, and the level of the catalytic solutions is comprised between 0 and 10% by weight, preferably between 0 and 1% by weight.

The known processes for hydroconversion of heavy feedstocks by slurry technology are ENI's EST operating at temperatures of the order of 400-420° C., under pressures of 10-16 MPa with a particular catalyst (molybdenite); Headwaters' (HC)3 operating at temperatures of the order of 400-450° C., under pressures of 10-15

MPa with Fe pentacarbonyl or Mo 2-ethyl hexanoate, the catalyst being dispersed in the form of colloidal particles; HDH and HDHPLUS® licensed to Intevep/PDVSA operating at temperatures of the order of 420-480° C., under pressures of 7-20 MPa, using a dispersed metallic catalyst; Chevron's CASH using a sulphide catalyst of Mo or W prepared by aqueous route; UOP's SRC-Uniflex operating at temperatures of the order of 430-480° C., under pressures of 10-15 MPa; VCC developed by Veba and belonging to BP operating at temperatures of the order of 400-480° C., under pressures of 15-30 MPa, using an iron-based catalyst; ExxonMobil's Microcat; etc.

All these slurry processes can be used in the process according to the invention.

Separation

All of the effluent originating from the hydroconversion is directed towards a separation section, generally into a high pressure high temperature (HPHT) separator, which makes it possible to separate a fraction converted to the gaseous state, a so-called light fraction, and an unconverted liquid fraction containing solids, a so-called residual fraction.

This separation section is preferably operated under operating conditions similar to those of the reactor which are in general a pressure of 2 to 35 MPa with a preferred pressure of 10 to 25 MPa, a partial hydrogen pressure varying from 2 to 35 MPa and preferably from 10 to 25 MPa and a temperature comprised between 300° C. and 500° C., preferably from 380° C. to 460° C. The residence time of the effluent in this separation section is 0.5 to 60 minutes and preferably 1 to 5 minutes. The light fraction contains mostly compounds boiling at a maximum temperature of 300° C., or even at a maximum temperature of 400° C. or 500° C.; they correspond to the compounds present in the gases, naphtha, light gas oil, or even heavy gas oil. It is pointed out that the cut contains mostly these compounds, as the separation is not carried out according to a precise cut point, rather it is similar to a flash separation. If reference were to be made to a cut point, it could be said to be situated between 200° and 400° or even 450° C.

The upcycling of the light fraction is not the subject of the present invention and these processes are well known to a person skilled in the art. The light fraction obtained after the separation can be subjected to at least one hydrotreatment and/or hydrocracking step, the objective being to bring the different cuts up to specifications (sulphur content, smoke point, cetane number, aromatics content, etc.). The light fraction can also be mixed with another feedstock before being directed towards a hydrotreatment and/or hydrocracking section. An external cut generally originating from another process existing in the refinery or optionally outside the refinery can be supplied before hydrotreatment and/or hydrocracking, advantageously the external cut is for example VGO originating from the fractionation of crude oil (straight-run VGO), VGO originating from a conversion, an LCO (light cycle oil) or an HCO (heavy cycle oil) from FCC.

Generally, the hydrotreatment and/or hydrocracking after the hydroconversion can conventionally be carried out via an intermediate standard separation section (with decompression) using, after the high pressure high temperature separator for example, a high pressure low temperature separator and/or atmospheric distillation and/or vacuum distillation. Preferably, the hydrotreatment and/or hydrocracking section is integrated directly into the hydroconversion section without intermediate decompression. In this case, the light fraction is sent directly, without additional separation steps and without decompression, to the hydrotreatment and/or hydrocracking section. The latter embodiment makes it possible to optimize the pressure and temperature conditions, avoids additional compressors and therefore minimizes the costs of additional equipment.

The residual fraction originating from the separation (for example via the HPHT separator) and containing the metals and a fraction of solid particles used as an optional additive and/or formed during the reaction can be directed towards a fractionation step. This fractionation is optional and comprises a separation under vacuum, for example one or more flash vessels and/or, preferably, vacuum distillation, making it possible to concentrate a vacuum residue rich in metals at the bottom of the vessels or column and to recover one or more effluents at the top of the column. Preferably, the residual fraction originating from the separation step without decompression is fractionated by vacuum distillation into at least one vacuum distillate fraction and one vacuum residue fraction, at least part and preferably all of said vacuum residue fraction being sent to the coking step, at least part and preferably all of said vacuum distillate fraction being subjected preferably to at least one hydrotreatment and/or hydrocracking step.

A small part of the liquid effluent(s) of the vacuum distillate fraction thus produced is usually directed towards the slurry hydroconversion unit, where it can be directly recycled into the reaction zone or it can then be used for the preparation of the catalytic precursors before injection into the feedstock. Another part of the effluent(s) is directed towards the hydrotreatment and/or hydrocracking section, optionally mixed with other feedstocks, such as for example the light fraction originating from the HPHT separator or a vacuum distillate originating from another unit, in equal or different proportions as a function of the quality of the products obtained. The objective of the vacuum distillation is to increase the yield of the liquid effluents for a subsequent hydrotreatment and/or hydrocracking treatment and therefore to increase the yield of fuel bases. At the same time, the quantity of the residual fraction containing the metals is reduced, thus facilitating the concentration of the metals.

Coking

The residual fraction originating from the separation without decompression (via the HPHT separator for example) and/or the vacuum residue fraction from the separation under vacuum (for example drawn off at the bottom of the vacuum distillation unit) are then directed towards a coking type thermal conversion step. The objective of this step is to concentrate the metals in the effluent to be subsequently treated by combustion, by reducing its quantity, and to maximize the yield of liquid effluents for the hydrotreatment and/or hydrocracking treatment.

The coking step can be carried out by delayed coking or by fluidized-bed coking (“fluid-coking” or “flexi-coking”). In the case of fluidized-bed coking the temperature of the reactor is greater than 490° C., preferably between 500-550° C., at atmospheric pressure. Preferably, the coking is carried out by delayed coking, in at least two maturation vessels. Before being sent into the maturation vessel, the feedstock is heated by heating ovens. The operating conditions are a temperature at the outlet from the feedstock heating ovens comprised between 460 and 530° C., preferably 480 and 510° C. and a temperature at the outlet from the maturation vessels greater than 420° C., preferably comprised between 430 and 490° C., and a pressure less than 0.5 MPa, preferably from 0.1 to 0.3 MPa. The recycling rate of the unconverted fraction from the maturation vessel is less than 20% by weight of the fresh feedstock, preferably less than 10% by weight. The coking is carried out under an inert atmosphere. The coking of the fresh feedstock is continuously ensured thanks to regular swapping between two maturation vessels, one being in the coking phase while the other is in the decoking phase. The delayed coking step produces a solid effluent containing coke (and the metals) and a liquid effluent. The liquid effluent is generally separated by distillation.

At least part, and preferably all of the liquid effluent produced during the coking and having a boiling point below a temperature comprised between 300 and 400° C. (Liquid Cycle Gas Oil, LCGO) can be sent to the hydrotreatment and/or hydrocracking section in a mixture with the light fraction from the HPHT separator and/or with an external cut.

The liquid effluent produced during coking having a boiling point greater than a temperature comprised between 300 and 400° C. (Heavy Cycle Gas Oil, HCGO) is preferably mixed with the heavy hydrocarbon feedstock upstream of the slurry hydroconversion section. It can also be sent to the hydrotreatment and/or hydrocracking section in a mixture with the light fraction from the HPHT separator and/or with an external cut. It can also be sent to the vacuum distillation step in a mixture with the residual fraction from the HPHT separator.

At least part, and preferably all of the solid effluent containing coke with a high concentration of metals is directed towards a moderate combustion step. Optionally, part of the solid effluent containing coke can be recycled as an additive in the hydroconversion step.

Combustion

The solid effluent containing coke is directed towards a step of combustion at a moderate temperature and in the presence of oxygen. Before the metals can be recovered by standard metal extraction processes described below, a preliminary step is necessary in order to separate the organic phase (the coke) from the inorganic phase containing the metals. Thus, the objective of the combustion step is to obtain ashes containing the metals which can be easily recovered in the subsequent metal recovery units, by burning the organic phase or carbon phase of the solid effluent at a temperature and a pressure which limit the vaporization and/or sublimation of the metals, in particular that of molybdenum (sublimation temperature of approximately 700° C. for MoO₃). Thus, the step of reduction of the organic phase consists of combustion at a moderate temperature in order to concentrate the metals, without any significant loss by vaporization and/or sublimation to fumes, in a mineral phase which can contain an organic phase proportion ranging from 0 to 100% by weight, preferably from 0% by weight to 40% by weight. The operating conditions of this combustion are in general a pressure of −0.1 to 1 MPa, preferably −0.1 to 0.5 MPa, a temperature of 200 to 700° C., preferably 400 to 550° C. The combustion takes place in the presence of air.

The gaseous effluent originating from the combustion requires purification steps in order to reduce the emission of sulphur and nitrogen compounds into the atmosphere. The processes used in a standard fashion by a person skilled in the art in the field of air treatment are implemented under operating conditions necessary to meet the standards in force in the countries where such a hydrocarbon feedstock treatment is carried out.

The solid originating from the combustion is a mineral phase containing all, or almost all, of the metallic elements contained in the extract, in the form of ashes.

The direct treatment of the solid effluent leaving the coking by a metal extraction method as described below without combustion displays an insufficient metal recovery rate.

Recovery of the Metals

The ashes originating from the gasification are sent to a step of extraction of the metals in which the metals are separated from each other in one or more sub-step(s). This recovery of the metals is necessary, as the simple recycling of the ashes in the hydroconversion step shows very weak catalytic activity. Generally, the step of extraction of the metals makes it possible to obtain several effluents, each effluent containing a specific metal, for example Mo, Ni or V, generally in the form of salt or oxide. Each effluent containing a catalyst metal is directed towards a step of preparation of an aqueous or organic solution based on the metal identical to the catalyst or its precursor, used in the hydroconversion step. The effluent containing a metal originating from the feed which cannot be valorized in the form of catalyst (such as vanadium for example) can be valorized outside the process.

The operating conditions, the fluids and/or extraction methods used for the different metals are considered to be known to a person skilled in the art and already used industrially, for example as described in Marafi et al., Resources, Conservation and Recycling 53 (2008)1-26, U.S. Pat. No. 4,432,949, U.S. Pat. No. 4,514,369, U.S. Pat. No. 4,544,533, U.S. Pat. No. 4,670,229 or US2007/0025899. The different known routes of extraction of metals generally include leaching by acid and/or basic solutions, by ammonia or ammonia salts, bioleaching by microorganisms, low-temperature thermal treatment (roasting) by sodium or potassium salts, chlorination or also the recovery of metals by electrolytic route. Leaching by acids can be carried out by inorganic acids (HCl, H₂SO₄, HNO₃) or organic acids (oxalic acid, lactic acid, citric acid, glycolic acid, phthalic acid, malonic acid, succinic acid, salicylic acid, tartaric acid, etc.). For basic leaching ammonia, ammonia salts, soda or Na₂CO₃ are generally used. In both cases, oxidizing agents (H₂O₂, Fe(NO₃)₃, Al(NO₃)₃, etc.) can be present in order to facilitate the extraction. Once the metals are in solution, they can be isolated by selective precipitation (at different pHs and/or with different agents) and/or by extraction agents (oximes, beta-diketone, etc.).

Preferably, the step of extraction of the metals according to the invention comprises leaching by at least one acid and/or basic solution.

Preparation of Catalytic Solution(s)

The metals recovered after the extraction step are generally in the form of salt or oxide. The preparation of catalytic solutions for producing organic or aqueous solutions is known to a person skilled in the art and has been described in the hydroconversion part. The preparation of the catalytic solutions relates in particular to the metals molybdenum and nickel, vanadium generally being valorized in the form of vanadium pentoxide, or in combination with iron, for the preparation of ferrovanadium, outside the process.

The recovery rate of metals upcycled in the form of catalyst for the slurry hydroconversion process or for vanadium is at least 50% by weight, preferably at least 65% by weight and more generally 70% by weight.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a process for hydroconversion of heavy petroleum feedstocks integrant a slurry technology without recovery of metals.

FIG. 2 describes a process for hydroconversion of heavy petroleum feedstocks according to the invention. The installation and process according to the invention are essentially described. The operating conditions described previously are not repeated.

In FIG. 1, the feedstock 1 feeds the catalytic slurry hydroconversion section A. This catalytic slurry hydroconversion section is constituted by an oven for preheating the feedstock 1 and the hydrogen 2 and by a reaction section constituted by one or more reactors arranged in series and/or in parallel, depending on the required capacity. The catalyst 4 or its precursor is also injected, as well as the optional additive 3. The catalyst 4 is maintained in suspension in the reactor, flows from the bottom towards the top of the reactor with the feedstock, and is removed with the effluent. The effluent 5 originating from the hydroconversion is directed towards a high pressure high temperature separation section B which makes it possible to separate a fraction converted to the gaseous state 6, a so-called light fraction, and a liquid/solid unconverted residual fraction 8. The light fraction 6 can be directed towards a hydrotreatment and/or hydrocracking section C. An external cut 7 generally originating from another process existing in the refinery or optionally outside the refinery can be supplied before the hydrotreatment and/or hydrocracking. The unconverted residual fraction 8 containing the catalyst and a fraction of solid particles used as optional additive and/or formed during the reaction is directed towards a fractionation step D. The fractionation step D is preferably a vacuum distillation making it possible to concentrate the metal-rich vacuum residue 10 at the bottom of the column and recover one or more effluents 9 at the top of the column. In this diagram showing valorization of a heavy feedstock by a slurry hydroconversion process used conventionally, the metal-rich vacuum residue 10 is valorized in the form of fuel with a very high viscosity or in the form of solid fuel after pelletization, for example to produce heat and electricity on site or off site or also in the form of fuel in a cement works. The metals are not recovered beforehand. One small part of the effluent or effluents 9 thus produced is(are) usually directed via the line 24 towards the slurry hydroconversion unit A where it can be directly recycled into the reaction zone or can then be used for the preparation of the catalytic precursors before injection into the feedstock 1 and another part towards the hydrotreatment and/or hydrocracking unit C via the line 25 mixed with the effluents 6 and/or 7 in equal or different proportions as a function of the quality of the products obtained.

In FIG. 2, the hydroconversion, HPHT separation, hydrotreatment and/or hydrocracking steps (and reference signs) and the vacuum distillation step are identical to FIG. 1. The vacuum residue 10 drawn off at the bottom of vacuum distillation unit D is directed towards a coking type thermal conversion step E in order to concentrate the effluent 10. The liquid effluent produced during the coking and having a boiling point less than a temperature comprised between 300 and 400° C. (LOGO) 11 can be sent to the hydrotreatment/hydrocracking section C via the line 22 mixed with the effluent 6 and/or 7. The liquid product having a boiling point greater than a temperature comprised between 300 and 400° C. (HCGO) 12 is preferably sent to the slurry hydroconversion section A via the line 23 mixed with the feedstock 1. It can also be sent to the hydrotreatment/hydrocracking section C via the line 28 mixed with the effluent 6 and/or 7, and/or towards the vacuum distillation step D via the line 29 mixed with the effluent 8. Part, and preferably all, of the solid effluent containing the coke 13 with a high concentration of metals is directed towards a step of reduction of the organic phase by combustion at a moderate temperature F in order to highly concentrate the metals, without significant loss by vaporization and/or sublimation to fumes. A smaller part of the solid effluent 13 can be sent as an additive 3 via the line 50 into the hydroconversion step A. The gaseous effluent originating from the combustion 14 requires purification steps (not shown) in order to reduce the emission of sulphur and nitrogen compounds into the atmosphere. The product 15 originating from the combustion F is a mineral phase containing all, or almost all, of the metallic elements contained in the solid 13, in the form of ashes. The product 15 is sent to a step of extraction of the metals G in which the metals are separated from each other in one or more sub-steps. The effluent 16 originating from the extraction G is made up of a molybdenum type metal in the form of salt or oxide. This effluent 16 is then directed towards a step of preparation H of a molybdenum-based organic or aqueous solution 18 identical to the catalyst 4 or to its precursor, part or all of which is recycled to the slurry hydroconversion step A via the line 40. The effluent 17 originating from the extraction G is made up of a nickel type metal in the form of salt or oxide. This effluent 17 is then directed towards a step of preparation I of a nickel-based organic or aqueous solution 19 identical to the catalyst 4 or to its precursor part or all of which is recycled in the slurry hydroconversion step A via the line 41. The effluent 20 originating from the extraction G is made up of a vanadium type metal in the form of salt or oxide. This effluent 20 can be valorized for example in the form of vanadium pentoxide, or in combination with iron, for the preparation of ferrovanadium.

In the preferred case of a slurry hydroconversion using a catalyst based on molybdenum and nickel, the hydroconversion utilizes a finely dispersed catalyst of nickel and molybdenum type with respective concentrations of 160 ppm by weight and 600 ppm by weight under hydrogen pressure. Given that the industrial unit has a capacity of 50,000 barrels a day and 90% annual capacity utilization, the quantity of nickel of molybdenum consumed per year is therefore 0.4 and 1.6 kt/year respectively. Given a nickel cost of 25 k$/t and a molybdenum cost of 60 k$/t, representative of the average costs observed on the metals market over the last 5 years, the operating cost is 100 million dollars per year.

The process according to the invention allows valorization of a large part of the metals, nickel and molybdenum, present in the unconverted fraction of the effluent originating from the slurry hydroconversion. The recovery rate of metals valorized in the form of catalyst for the slurry hydroconversion process is at least 50% by weight, preferably at least 65% by weight, and more generally 70% by weight. This recycling of metals therefore makes it possible to reduce the operating cost from 100 million dollars per year to 30 million dollars per year. Firstly, the thus-achieved saving of 70 million dollars makes it possible to pay for the additional investments necessary for the recovery of these metals. In addition, the vanadium present in the heavy feedstock at 400 ppm by weight can be valorized in the form of ferrovanadium. Given a recovery rate of at least 50% by weight, preferably at least 65% and more generally 70% by weight, sales of vanadium are estimated, given an observed average cost of 40 k$/t on the metals market over the last 5 years, at 12 million dollars per year. These sales also make it possible to cover the initial additional investment necessary for the recovery of these metals.

The recovery of these metals from the unconverted residual fraction makes it possible to reduce the overall quantity of nickel and molybdenum used and thus to reduce the environmental impact of the slurry hydroconversion process. Given a recovery of 70% by weight of the metals present at the inlet to the reaction zone, the quantity of supplementary catalyst is reduced to 0.1 t/yr in the case of nickel and 0.5 t/yr in the case of molybdenum compared with 0.4 t/yr and 1.6 t/yr without recycling. 

1. Process for hydroconversion of heavy petroleum feedstocks containing metals comprising: a) a step of hydroconversion of the feedstock in at least one reactor containing a slurry catalyst containing at least one metal, and optionally a solid additive, b) a step of separation of the hydroconversion effluent without decompression into a so-called light fraction containing the compounds boiling at a maximum temperature of 500° C. and a residual fraction, b′) optionally a fractionation step comprising a separation under vacuum of said residual fraction as obtained in step b), and a vacuum residue with a high concentration of metals is obtained, c) a step of coking of said residual fraction as obtained in step b) and/or of said vacuum residue as obtained in step b′) making it possible to obtain a solid effluent containing coke, d) a step of combustion of said solid effluent containing coke at a temperature comprised between 200 and 700° C. making it possible to obtain ashes with a high concentration of metals, e) a step of extraction of the metals from the ashes obtained in the combustion step, f) a step of preparation of metallic solution(s) containing at least the metal of the catalyst which is/are recycled(s) as catalyst in the hydroconversion step.
 2. Process according to claim 1 in which said so-called light fraction originating from the separation step without decompression is subjected to at least one hydrotreatment and/or hydrocracking step.
 3. Process according to claim 1, in which the coking step is delayed coking and takes place at a temperature at the outlet from the feedstock heating ovens comprised between 460 and 530° C., preferably 480 and 510° C., and a temperature at the outlet from the maturation vessels greater than 420° C., preferably comprised between 430 and 490° C., and a pressure less than 0.5 MPa, preferably of 0.1 to 0.3 MPa, under an inert atmosphere.
 4. Process according to claim 1 in which the combustion step takes place at a temperature of 400 to 550° C., in the presence of oxygen.
 5. Process according to claim 1 in which the combustion step takes place at a pressure of −0.1 to 1 MPa, preferably −0.1 to 0.5 MPa and at a temperature of 400 to 550° C., in the presence of oxygen.
 6. Process according to claim 1, in which the step of extraction of the metals comprises leaching by at least one acid and/or basic solution.
 7. Process according to claim 1 in which said residual fraction originating from the separation step without decompression is fractionated by vacuum distillation into at least one vacuum distillate fraction and one vacuum residue fraction, at least part and preferably all of said vacuum residue fraction being sent to the coking step, at least part and preferably all of said vacuum distillate fraction being subjected to at least one hydrotreatment and/or hydrocracking step.
 8. Process according to claim 1 in which part of the solid effluent containing coke from the coking step is recycled as an additive in the hydroconversion step.
 9. Process according to claim 1 in which the heavy petroleum feedstock is a hydrocarbon feedstock containing at least 50% by weight of product distilling above 250° C. and at least 25% by weight distilling above 350° C., and contains at least 50 ppm by weight of metals, at least 0.5% by weight of sulphur and at least 1% by weight of asphaltenes (heptane asphaltenes).
 10. Process according to claim 1 in which the heavy petroleum feedstock is chosen from petroleum residues, crude oils, topped crude oils, deasphalted oils, asphalts or deasphalting pitches, derivatives from petroleum conversion processes, bituminous sands or derivatives thereof, bituminous shales or derivatives thereof, or mixtures of such feedstocks.
 11. Process according to claim 1 in which the hydroconversion step takes place at a pressure of 2 to 35 MPa, preferably 10 to 25 MPa, a partial hydrogen pressure of 2 to 35 MPa, preferably 10 to 25 MPa, a temperature comprised between 300° C. and 500° C., preferably from 420° C. to 480° C. and a contact time of 0.1 hour to 10 hours, preferably 0.5 hour to 5 hours.
 12. Process according to claim 1 in which the slurry catalyst is a sulphide catalyst containing at least one element chosen from the group formed by Mo, Fe, Ni, W, Co, V, Ru.
 13. Process according to claim 1 in which the additive is chosen from the group formed by the mineral oxides, supported spent catalysts containing at least one Group VIII element and/or at least one Group VIB element, carbonaceous solids with a low hydrogen content or mixtures of such additives, said additive having a particle size of less than 1 mm 